AT&T IP Flexible reach

I have AT&T IP Flexible Reach Business in a box T1 service. Currently I have 4 out of 7 lines from analog port of router are connected to the old Analog PBX. I want to try Asterisk server.
I have already installed Asterisk server and is working fine for internal calling.
My question is what hardware do I need to start using Asterisk for outside calling?